My way to test the impact of cables on my system was taught to me by an old Tibetan monk and I also use it for testing the rest of my material: I listen.
What changing one single power cable on, for example, a CD player does to the sound was even immediately noticed by my wife, who's anything but a mad audiophile.
Rischa, what is a fast cable? Hard to describe but, for example, when I hook up my Jadis monos (over designed by all means with its 2400 transfos for its 80 watts) with the Sunyata KC VX1, the sound is darker and less dynamic than how it is when hooked up with the Sunyata Pythons.
I agree with all those who recommend changing the electrical greed cables but it's not in my capacity to do so, not even in the apartment where I live. If I could, I would. Nevertheless I did change the wall sockets and the fuses in the electrical cupboard and it all helps for a better, clearer sound.
With the entire system hooked up to the Shunyata Hydra 8 V2, there's no longer that difference between what is referred to as "day listen" and "night listen".
Enjoy.